a) Field of the Invention
This invention relates to a method of polymerizing vinyl chloride monomer alone or together with a vinyl monomer copolymerizable therewith into a polymer having excellent physical properties in a high yield by the use of a specifically limited polymerization initiator.
b) Related Art Statement
There have been used polymerization initiators, such as tertiary butylperoxy neodecanoate (hereinafter, abbreviated as BND), 3,5,5-trimethylhexanoyl peroxide (hereinafter, abbreviated as NPO), di(2-ethylhexyl) peroxy dicarbonate (hereinafter, abbreviated as OPP) and the like, each of which has a 10-hour half-life period temperature within the range of 40.degree.-65.degree. C. in its 0.1 mol concentration solution in benzene, in the polymerization of vinyl chloride monomer alone or together with a vinyl monomer copolymerizable therewith.
However, when these polymerization initiators are used alone, there are economical problems such that the polymerization efficiency is low unless a relatively high polymerization temperature is used, and the polymerization reaction cannot be completed unless a large amount of the polymerization initiator is used. In order to eliminate these drawbacks and to enhance the productivity of vinyl chloride homopolymer or copolymer by shortening the polymerization cycle, a polymerization initiator, such as diisobutyryl peroxide (hereinafter, abbreviated IBPO), which has a higher activity at low temperature than that of the above described conventional polymerization initiator, has been developed and used in combination with the conventional polymerization initiator (refer to Japanese Patent Application Publication No. 56-50,892).
That is , it has been attempted to carry out a constant rate polymerization reaction by the use of the above described polymerization initiator, such as IBPO or the like, in combination with the above described conventional polymerization initiator, such as BND or the like, which polymerization initiator, such as IBPO or the like, has a higher activity at low temperature than that of the conventional polymerization initiator, such as BND or the like, and is used as a rapid-active polymerization initiator capable of giving a high reaction rate in the initial stage of the polymerization reaction, and which conventional polymerization initiator, such as BND or the like, is used as a delayed-active polymerization initiator capable of giving a high reaction rate in the latter stage of the polymerization reaction.
Such rapid-active polymerization initiators include IBPO, acetylcyclohexylsulfonyl peroxide (hereinafter, abbreviated as ACSP), cumylperoxy neodecanoate (hereinafter, abbreviated as CND) and the like, each of which has a 10-hour half-life period temperature of not higher than 40.degree. C.
Recently, a constant rate polymerization has been investigated by using a combination system of a rapid-active polymerization initiator and a delayed-active polymerization initiator, and by adjusting the amount of these initiator used. However, the conventional rapid-active polymerization initiator has not a satisfactorily high activity, and its effect for shortening the polymerization time is low even in the used together with a delayed-active polymerization initiator. Therefore, the development of a polymerization initiator having a higher activity at low temperature than that of the above described conventional rapid-active polymerization initiator has been eagerly demanded.
Further, the quality of a polymer has recently become important in addition to the high productivity, and the development of a polymerization initiator having a high activity and being able to produce a polymer having excellent physical properties is eagerly demanded.
When the above described conventional rapidactive polymerization initiator is used, the resulting polymers have not always satisfactorily excellent physical properties. For example, when a polymer obtained by a polymerization using IBPO is formed into a soft resin shaped article, a large amount of fish-eyes (hereinafter, abbreviated as FEs) are formed.
When ACSP is used, a polymer having a large amount of FEs is formed, and moreover the resulting polymer is poor in the thermal stability and discolors. When CND is used, a fairly strong offensive smell peculiar to CND is generated due to its decomposition product during the processing of the resulting polymer.
The presence of FEs deteriorates the appearance of shaped articles produced from vinyl chloride homopolymer or copolymer resin, and hence the shaped article is very low in value as a merchandise. Moreover, the offensive smell of the polymer deteriorates the working environment, and injures the health of operators. That is, the generation of offensive smell is a serious social problem.
The inventors have made various investigations for a long period of time with respect to the drawbacks of the above described conventional rapid-active polymerization initiator, and found out that, when a specifically limited polymerization initiator is used as a rapid-active polymerization initiator, a polymer can be obtained in a high yield, and further the resulting polymer is free from FEs and from offensive smell and has high thermal stability, particularly high resistance against discoloration. As the result, the present invention has been accomplished.